1. Field of the Invention
The present invention relates to a method of recording information signals on an information signal recording medium formed with a plurality of circular tracks, and more specifically to a method of recording information signals scrambled with scrambling signals.
2. Description of the Prior Art
In general, in an optical disk such as a compact disk (CD), digital signals are recorded by forming concave and convex portions (referred to as pit and land portions) along tracks formed on the disk, and the light reflected from the pit and land portions is received by a quadrant optical sensor housed in an optical head, and further converted into electric signals to read information signals from the optical disk.
For focusing the detection light onto the optical disk, an objective lens of the optical system housed in a pickup is so controlled as to follow the surface deflection of the disk in accordance with an astigmatic method, for instance. In addition, for tracking to eccentric tracks, the pickup is so controlled as to follow the tracks in accordance with a three-beam method, push-pull method, heterodyne method, etc.
In the focusing and tracking control, the respective output signals of the double- or quadrant-divided optical sensor are calculated to obtain a focusing control signal and a tracking control signal for servo-controlling.
A laser beam emitted by the pickup produces a phase difference between the beam reflected from the pit portion and the beam reflected from the land portion, so that it is possible to obtain reproduced signals on the basis of the difference in reflected light intensity caused by the interference effect and then incident upon the optical sensor. In the case of a compact disk, data is recorded by forming pit and land pattern on the basis of EFM (eight to fourteen modulation) signals. Therefore, the recorded data can be reproduced by binarizing the reproduced signals modulated on the basis of the light intensity change along the pit and the land portions, and further demodulated into digital signals.
In the signal recording system, two systems, that is, a CAV (constant angular velocity) system in which the disk angular velocity is kept constant and CLV (constant linear velocity) system in which the track linear velocity is kept constant are so far known. In the case of the CAV system, the number of sectors of each track is equal to each other, and all the tracks are so formed that the sector heads of all the tracks are perfectly arranged on the radial lines extending from the disk center.
Further, in the case of the CLV system, since the track linear velocity is constant, although the sector heads of all the tracks do not match each other on the disk, there exists some cases where the sector heads of a part of the adjacent tracks are arranged along on the same radial line extending from the disk center.
Under these circumstances, in the case where a great quantity of the information signals have the same content such as music intermissions, no-music sections, no-image sections, etc. are recorded for instance when music or image information signals are recorded, the recorded information signals are scrambled with scrambling signals in general in order to prevent the signals of the same pit and land shape or arrangement from being recorded in the adjacent tracks.
The scramble procedure as described above is adopted to prevent the synchronizing signal for synchronizing the sector heads of information signals from being generated in the recorded data as a pseudo-synchronizing signal, that is, to improve the DSV (digital sum variation) controllability of the EFM signal. That is, the information signals and scrambling signals referred to as M (maximum) period sequence are scrambled with each other, and then the scrambled signals are recorded as the information signals. Here, the M period sequence used for the scrambling procedure is defined by cyclic codes represented by (2.sup.x -1) units of 0 or 1.
For instance, the prior art scrambling means adopted in the conventional CD-ROM outputs the M period sequence of cyclic codes of (2.sup.15 -1=32767) represented by 0 or 1. Further, information signals are scrambled with the cyclic codes by using the same initial value (code) for each sector.
In the present tendency of the optical disk, the disk capacity and disk density are both increased more and more. In the prior art scrambling means as described above, however, when the information signals having the same content are recorded at the same positions at which the sector heads are arranged in the radial lines extending from the disk center, since the shape at the pit portion matches the shape at the land portion, correlation between both the portions increases, with the result that an amplitude of the tracking error signal is reduced and thereby the S/N (signal to noise) ratio decreases, thus causing a problem in that the tracking control cannot be executed stably.